What the latest research shows about indoor heatstroke in Japan

A graphic from a recent TV segment on TV Asahi's Morning Show have been sitting with me all day. it's a visualization of some of the findings of a joint study by the University of Tokyo Graduate School of Medicine and the Tokyo Metropolitan Medical Examiner’s Office, and the findings are honestly shocking. 

The chart looked at 1,295 indoor heatstroke deaths. What stood out immediately was how many of these tragedies happened in homes where the air conditioner was either off, broken, or not installed at all. Nearly 45% of cases occurred with the AC switched off, and another 29% in homes without any unit installed. Even among the small percentage where the AC was technically “on,” they were set to the wrong setting and / or weren’t cooling properly due to dust or mechanical issues.

These findings paint a very clear picture: in recent years, heatstroke has become an indoor danger, not just an outdoor one. Air conditioning is one of the strongest protective factors we have. Not using it, whether by choice, misunderstanding, or lack of access, dramatically increases the risk of death. These numbers aren’t just statistics; they’re a reminder to use our own air conditioners without hesitation as Japan's summers steadily grow hotter.